Electromagnetic induction apparatus



Nov. 18, 1952 c. D. cooK, JR

ELECTROMAGNETIC INDUCTION APPARATUS 3 Sheets-Shes?l 1 Filed Jan. 13.1948 I1*1\/e1"16or` Clinton D. Cook ,J1^.,

His Attorneg.

Nov. 18, 1952 C. D. COOK, JR

ELECTROMAGNETIC IND UCTION APPARATUS 3 Sheets-Sheet 2 Filed Jan. 13,1948 Inventor: Clinton D. Cook, JP.,

by His Attorney.

Nov. 18, 1952 C. D. COOK, JR

ELECTROMAGNETIC INDUCTION APPARATUS 3 Sheets-Sheet 5 Filed Jan. 15, 1948Inventor: Clinton DCOOk, Jn,

I-Is Attorney.

Patented Nov. 178, 1952 ELECTROMAGNETIC INDUCTION APPARATUS Clinton D.Cook, Jr., Shelburne, Vt., assignor to General Electric Company, acorporation of New York Application January 13, 1948, Serial No. 1,935

(Cl. F75-358) 2 Claims.

This invention relates to an electromagnetic induction apparatus andmore particuarly to improvements in transformers and to their method ofconstruction.

Heretofore, electromagnetic induction apparatus such as transformershave been provided with molded casings of various materials such asPortland cement or concrete or various synthetic resins and solventlessvarnishes. However, none of these constructions has been satisfactorybecause the various materials which have been used have had one or moreof the following defects, namely: they have been hydroscopic; or havehad low insulation value; or they crack during the initial curingperiod; or they crack during aging at or above normal operatingtemperatures; or they crack as a result of hot and cold cycles; or theyrequire excessive molding pressure which distorts the coils, cores, andwindings; or they are difficult to cure; or they form voids in thematerial; or they have excessive shrinkage with low impact strength andmodulus elasticity; or they attack the copper from which the coils aremade; or they stick to the mold; or, in general, they have poormoldabi'lity.

I have discovered, however, that the material known as GR-I (Governmentrubber isobutylene) is a nearly perfect material for forming both themajor insulation between the windings of such apparatus themselves,between the core and the windings, and for forming the outer casing ofthe apparatus. The raw material, which is cured in a manner similar tothe vulcanization of rubber during the molding operation, is a copolymerof a high proportion of isobutylene and a low proportion of isoprene. Ithas a dielectric strength of at least 150 volts per mil at continuoustemperatures of 85 C. with part time temperatures of 95 C. and shorttime temperatures (l second) of 150 C. It has a power factor lower than3%, is not affected by corona and has 'good surface arcing'characteristics. Furthermore, it has a relatively high heat transferability of .l B. t. u. through a cubic foot per hour per degreeFahrenheit temperature difference between opposite faces. It is toughand resilient and will not crack due to expansion of embedded coppercoils throughout a temperature range of 40 C. to |100 C. and testsindicate an outdoor life of 25 years.

However, I do not wish to be limited to butyl rubber and I comprehendthe use of all rubberlike materials which may be thermoplastic, orthermoplastic, and thermosetting, which are at least somewhat fluidbefore curing and which result in a firm resilient insulating structuresimilar in characteristics to that produced by butyl rubber. Forexample, I have in mind plastesol type materials composed of modifiedvinyl chloride formulations.

An object of the invention is to provide an electromagnetic inductionapparatus havingla resilient molded casing which also provides the majorinsulation and mechanical support of the transformer parts.

Another object of the invention is to reduce the size and cost ofelectromagnetic induction apparatus.

A further object of the invention is to provide a transformer casingwhich is equally suitable for indoor and outdoor use.

An additional object of the invention is to improve the appearance anddurability of electromagnetic induction apparatus.

An added object of the invention is to provide electromagnetic inductionapparatus with a homogeneous resilient molded casing and insulationwhich has high dielectric strength and low power factor over hightemperature ranges which is substantially unaffected by corona andsurface arcing, which has good heat transfer properties and longweather-resistant outdoor life.

The invention will be better understood from the following descriptiontaken in connectionv with the accompanying drawing and its scope will bepointed out in the appended claims.

In the drawing, Fig. 1 is a perspective view of a high voltage currenttransformer embodying the invention, Fig. 2 is a perspective view of amold for making the transformer shown in Fig. 1, Fig. 3 is an explodedperspective view showing the top and bottom halves of the mold separatedand with the parts of the transformer also separated, Fig. 4 is atransverse sectional view through the mold and transformer, Fig. 5 is anenlarged vertical section through the transformer shown in Fig. 1, Fig.6 is a perspective view of a,

modification and Fig. '7 is a horizontal sectional view through themodification shown in Fig. 6.

Referring now to the drawing and more particularly to Fig. 1, thecurrent transformer comprises a resilient molded dielectric body orcasing I through the center of which passes a heavy conducting bar 2,which is preferably made of copper and which constitutes the primarywinding and its terminals. The transformer is provided with mountingfeet 3 and with secondary winding terminals 4 which are recessed in acavity 5 in the insulating body i. A polarity marker 8 is moldeddirectly into the body I. Between the ends of the primary bar 2, whichare normally at the same relatively high line potential, and the parts 3and 4, which are normally near ground potential, the main body I isfiuted or provided with one or more integral ridges or petticoats 1 forincreasing the creepage distance along the surface of the body I. Aline8 on the surface of the body I corresponds with the plane of separationof the two halves of a mold in which the body I is formed.

The above-mentioned mold is shown in Fig. 2 as comprising what may bereferred to asa top half 9 and a bottom half I0, whose plane of junctureor separation is also represented by the line 3. The two halves of themold are held tightly together by any suitable means such as c clamps Ilwhich cooperate with complementary integral sidewise extensions on thetwo halves of the mold. A suitable material for the mold is cast steel,and it has been found that a cast inner surface is suitable for andgives good molding results and good appearance of the molded productwithout the necessity of machining of the inner surface of the mold. Thetop half 9 of the mold is provided with a filler opening I2 in which isinserted a bushing or coupler I3 for making tight connections to thereservoir (not shown) for the material which is to be molded. Assuitable places around the mold, the two adjoining faces are providedwith complementary recesses or notches I4 for making it easier to prythe two halves of the mold apart after the transformer body I has beencured and the c clamps II have been removed.

In Fig. 3 the two halves of the mold are shown separated and it will beseen that the top part 3 carries dowel pins I5 for insertion in holes I6in the bottom part I so as to assure proper alignment of the two partsof the mold when they are brought together. Between the two halves ofthe mold is shown a core and coil assembly comprising a generallyoval-shaped magnetic core I1 on which are wrapped a number of coils ofwire I 3, i8 and 20 which are interconnected to form the secondarywinding of the transformer.

In assembling the parts shown in Fig. 3, preparatory to molding the mainbody I, the primary bar 2 is inserted in the center opening through thecore and coil assembly and its edges are fitted into slots 2I in thelower half of the mold. The core and coil assembly is centered on thebar 2 and spaced therefrom by suitable supporting blocks'on oppositesides. Two of these blocks are shown at 22 and 23 and they are providedwith grooves which embrace the secondary terminals 4. 'Ihese blocks 22and 23 fit snugly into a cavity 24 in the mold and theythus cause theformation of the secondary terminal cavity or recess in the main body Ias shown in Fig. 1. The mounting feet 3 are supported in notches 25 inthe mold parts. The proper spacing of the mounting feet 3 is obtained bymeans of a spacing block 28 and the ends of the feet and the spacingblock 23 are in turn securely held in position by plates 21 which arescrewed into the two halves of the mold.

The primary bar 2 is properly centered lengthwise in the mold by meansof end plates 28 which are attached to the lower half of the mold acrossthe outer open ends of slots 2 I.

Fig. 4 clearly shows how the main body I is no only molded around theprimary bar 2 but is also formed between the primary bar or winding 2and the core and coil assembly so that the same material which forms theouter surface or housing for the apparatus also serves as its maiorinsulation between its different voltage parts.

Fig. 4 also shows how the mounting feet 3 are formed from the ends of astrap 28 which is wrapped around the core underneath the secondarywinding.

The reason the boundary plane between two halves of the mold isperpendicular to the plane of the primary bar 2 is to make it easier toseparate the two halves of the mold after the main body I has been curedand also so as to prevent separation oi' the material of the main body Ifrom the primary bar 2.

In the molding operation, the raw material known as GR-I is compoundedwith various suitable ingredients, such as are used in vulcanization ofrubber, to form a molding compound which is vulcanizable at elevatedtemperatures to form a good ozone and oxygen resistant material which isparticularly suitable for use as a dielectric having exceptional agingproperties. The molding compound is forced into the mold through thebushing I3 at a suitable pressure, such as 600-1000 pounds per squareinch, so as to entirely ll the free spaces in the mold. The material isthen cured for a suitable length of time at elevated temperatures; thiscuring or vulcanization being essentially a thermosetting phenomenoncaused by polymerization.

Returning briefly to Fig. 3, the parts of the mold which form thepolarity mark are indicated at 30 and the parts of the mold which formthe integral fluted portions or ridges on the main body l are indicatedat 3 l.

The sectional View shown in Fig. 5 illustrates more clearly the unitaryor integral nature of the main body I as an outer housing, as the majorinsulation between the primary bar 2 and the core I1, and as the ridgemembers 1 for increasing the creepage distance between the bar 2 and themounting feet 3, and between the bar 2 and the secondary terminals. Inthis figure the secondary coils are not visible because the section istaken through the front vertical center line.

A supporting plate 32 to which the turned over ends of the mounting feet3 have been attached in any suitable manner such as by welds 33 has beenillustrated in Fig. 5.

In the modification shown in Figs. 6 and 7,

there is a molded main body 34 which, unlike body I in Figs. 1 to 5,serves as the protective covering or housing of the apparatus and alsoas the major insulation between a multiturn pril mary winding 3B on theone hand, and a multias by brazing. The secondary winding terminals` areshown at 40 in Fig. 6. A suitable mounting or base plate 4I, preferablyof metal, is provided.

Due to the resilient properties of the bodies I and 34, the transformersare exceptionally sturdy and they will stand very rough treatmentwithout chipping or cracking or otherwise in- Juring them.

As shown in Fig. 6, around the main body 34, there is an equitorial line42 which indicates the plane of juncture of the two halves of the mold(not shown) in which the body 34 is formed, and it will be seen that theplane of this line bears the same relation to the plane of the terminals39 and 40 as exists between the plane of the line 8 and the plane of theprimary bar 2 in Fig. 1.

While there have been shown and described particular embodiments of theinvention, it will be obvious to those skilled in the art that changesand modifications can be made without departing from the invention and,therefore, it is aimed in the appended claims to cover all such changesand modications as fall within the true spirit and scope of theinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. An outdoor bar type current transformer, comprising, in combination,a closed magnetic core, a low voltage secondary winding surrounding saidcore, a straight conducting primary bar extending through said core, anda resilient body of isobutylene copolymerized with isoprene in whichsaid core and secondary Winding and the center of said bar embedded, theends of said bar extending out beyond said body and constituting highvoltage terminals for said transformer, said body having integral ridgessurrounding said bar for increasing the electrical creepage distance ofthe surface of said body relative to its overall outside dimensions.

2. The method of making a high voltage current transformer whichcomprises, equipping a magnetic core with an inner low voltage secondaryand an outer high voltage primary winding, said windings being spacedapart from each other, said high voltage primary winding having a pairof rectangular cross section bar type bare metal terminals extending inopposite directions in the same plane from the ends of said primarywinding, placing said core and winding in a mold having two halves whichare separable along a plane which bisects said terminals perpendicularto their plane of extension, said mold halves having registering grooveswhich closely receive said terminals, forcing a plastic molding compoundof a copolymer having a high proportion of isobutylene and a lowproportion of isoprene into said mold under a pressure of 600 to 1000pounds per square inch until all the space in said mold not occupied bysaid core, said windings and said terminals is filled with saidcompound, elevating the temperature of said mold substantially aboveroom temperature for a predetermined length of time so as to cure saidcompound by thermosetting it, separating the two halves of said moldalong said plane of separation so as to place minimum strain on themolded material adjacent the surface of said terminals, and removing themolded transformer from said divided mold.

CLINTON D. COOK, JR.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 894,620 Frank July 28, 19081,333,004 Vaughn Mar. 9, 1920 1,790,981 Fischer Feb. 3, 1931 2,065,934Deutschmann Dec. 29, 1936 2,163,798 Mucher June 27, 1939 2,246,167DEntremont June 17, 1941 2,251,351 Cooper Aug. 5, 1941 2,297,605 CamilliSept. 29, 1942 2,329,346 Goff Sept. 14, 1943 2,382,199 Brink Aug. 14,1945 2,385,460 Omansky Sept. 25, 1945 2,391,038 Rifenbergh Dec. 18, 19452,428,275 Frankwich et al. Sept. 30, 1947 2,436,636 DEntremont Feb. 24,1948 2,456,219 Shaheen Dec. 14, 1948 2,464,029 Ehrman Mar. 8, 1949FOREIGN PATENTS Number Country Date 426,324 Great Britain Jan. 1, 1934OTHER REFERENCES Article: Some Recent Advances in Industrial Plastics,Journal of Scientific Instruments, pages 129-136, vol. 19, September1942. 217General Electric Review, April 1943, pages 215-

